Intra-articular migration and activation of neutrophils may play a principal role in the joint erosion of inflammatory arthritis. DNA microarrays provide a means to profile gene expression in neutrophils from inflamed joints of patients with arthritis. Gene profiling may identify neutrophil regulators of intra-articular inflammation, and define key similarities and differences among inflammatory arthridities. The arthritis in patients with familial Mediterranean fever (FMF) is caused by mutations in MEFV, a gene encoding an inflammatory regulator that is specifically expressed in myeloid cells. FMF arthritis is unusual in that most inflammatory cells are neutrophils, and episodes of arthritis are transient. It therefore represents a unique human model to uncouple the initiation phase of synovitis from the chronic phase. Three specific aims are proposed: First, we will use immunohistochemistry and ELISAs to define the nature of intra-articular leukocyte infiltrates and cytokine profiles in FMF arthritis. These data will be compared with known profiles in other forms of arthritis. Second, we will perform microarray analysis from collected RNA samples of neutrophils form the active joints and peripheral blood of patients with period (FMF), chronic (rheumatoid and psoriatic), reactive, and infectious arthritis and from peripheral blood neutrophils of controls. Differentially expressed genes will be analyzed, with particular attention to identifying regulators of inflammation and defining subphenotypes within a specific disease. Third, we will test the functions of specific neutrophil gene products in modulating leukocyte adhesion and signaling. The MEFV gene performed to determine whether pyrin, will be expressed in myeloid cell lines, and microarray analysis of RNA from the cells will be differentially expressed known or novel gene products in FMF or other forms of arthritis will be tested in assays of leukocyte adhesion, transendothelial migration, chemotaxis, and other functions. These studies will define mediators of intra-articular neutrophil migration and activation, and may provide insights into the mechanisms that regulate leukocyte recruitment in other forms of inflammation.